Headspace versus Purge and Trap

How then do the techniques differ For this, the terms recovery and sensitivity must be defined. For both methods, the recovery depends on the vapour pressure, the solubility and the temperature. The effects of temperature can be dealt with because it is easy to increase the vapour pressure of a compound by raising the temperature during the vaporization step. With the P T technique, the term percentage recovery is used. This is the amount of a compound which reaches the gas chromatograph for analysis relative to the amount which was originally present in the sample. If a sample contains 100 pg benzene and 90 pg reach the GC column, the percentage recovery is 90%. In the static headspace technique, a simple expression like this cannot be used because it is possible to use a large 

A comparison with actual concentration values makes the differences between the static headspace and P T techniques very clear. The percentage recovery for 

For a larger injection (0.5 mL) using cryofocussing, the quantities injected are 1.2, 

6 and 0.4ng. The P8dT technique is therefore more sensitive than the static headspace procedure for these volatile halogenated hydrocarbons by factors of 4.1, 5.8, 7.2 and 9.3 (Table 2.13). 

Substance Lower application limits (pg/L) for headspace Lower application limits (pg/L) for purge and trap 

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